Term monetary aggregate Definition: Any of four basic measures of money, or liquid assets for the economy--M1, M2, M3, and L. The Federal Reserve System, as part of their regulatory duties, regularly publish these four monetary aggregates. The smallest, M1, is used as THE medium of exchange in the economy. However, M2 provides savings that are easily converted to M1 and is considered by many as the best measure of spendable assets.